[14.14] Exploration of the Neptune System

Voyager 2, ground-based, and HST studies leave many
questions regarding the Neptune system. How deep is the
zonal structure? What is the composition of discrete
features, and of the atmosphere as a function of altitude?
Why are the winds and thermal structure on Uranus and
Neptune similar, when the internal heat sources are so
different? Why are the magnetic fields more asymmetric in
ice giants than in gas giants? What is Triton's atmospheric
composition and structure, and how has it changed since
Voyager? Is Triton's surface extremely young? Is there
convection in Triton's interior? How does composition relate
to geologic terrain? How do ring arcs remain stable? Do
Neptune's inner satellites show the effect of extreme tidal
stress?

Significant progress in understanding the Neptune system has
been made with Earth-based telescopes, and there is much
work that remains to be done with such facilities. High
angular resolution (HST, AO, NGST) studies will grow in
importance, as will observations in new wavelength regimes
(e.g. SIRTF). However, the answers to many of the questions
require observations made from within the Neptune system.
These include: 1) high spatial resolution images spanning a
wide range of solar phase angles for surface, cloud, and
ring studies; 2) high spatial resolution spectra for
compositional mapping; 3) UV and radio occultations for
atmospheric sounding; 4) resolved thermal imaging for
atmospheric and surface energetics; and 5) in situ particles
and fields measurements for magnetic and magnetospheric
studies.

A recent NASA study (C. Porco et al., 1999) gave a Neptune
System mission a top ranking for rich scientific yield and
connections to astrophysical problems outside the Solar
System (pre-biotic chemistry on Triton; local extrasolar
planet analog). A Neptune mission's unmatched diversity of
science return should place it at the top of the queue for
outer planet exploration.